The invention relates generally to transformers, and deals more particularly with a transformer formed in conjunction with a printed circuit board.
Transformers are widely used today for power supplies, power converters and other circuits where electrical/ground isolation, impedance matching or voltage transformation are required. Known transformers comprise a ferrite core and primary and secondary windings wrapped around the core. Typically the core is toroidal in shape, either round or square. The primary and secondary windings are wrapped around the sidewalls of the core and either interlaced with each other or wrapped around separate sections of the core. There are various known techniques to form the windings. For example, the windings can be simple copper wires wound around the core with the free ends joined and soldered to other circuitry as required by the application.
U.S. Pat. No. 4,847,986 discloses another transformer which is formed with a printed circuit board. The core is mounted onto a printed circuit board. Underneath the core, elongated printed conductors form segments of respective windings. Metallic wires are contoured over the top and two sides of the core, and are wire bonded to ends of respective printed conductors to form continuous strings of primary and secondary windings which surround the core. While this technique has the advantages of low profile and conjunction with a printed circuit board, further improvements are desirable to lower the cost of construction.
European patent application #91309527.9 also discloses a core mounted onto a printed circuit board. Underneath the core, elongated printed conductors form segments of respective windings. Metallic strips are contoured over the top and two sides of the core, and are surface bonded to ends of respective printed conductors to form continuous strings of primary and secondary windings which surround the core. While this technique has the advantages of low profile and conjunction with a printed circuit board, further improvements are desirable to lower the cost of construction.
Accordingly, an object of the present invention is to provide a transformer (or inductor) formed in conjunction with a printed circuit board but with lower cost of construction than and comparable electrical and thermal performance as the foregoing prior art.